Laser pointing devices have been widely used on firearms to allow the shooter to accurately aim the weapon without using the weapons sights, and are used in military type training systems to simulate an aimed shot. They have also been used in many commercial products and as aids in testing products, also range finders, laser designators, and the like.
The most common firearm application is to mount a laser on a weapon, providing adjustment so the laser can be aligned with the sights and use the laser beam to point the weapon at a target while the trigger is being pulled. Once the shot is fired, the alignment of the laser relative to the sights does not come into play since the bullet is on its trajectory to the target. The patents also claim the mounting and adjustments isolates the laser from the weapons shock which means the laser assembly is designed to move relative to the weapon during the high G shock event from firing the weapon.
The Multiple Integrated Laser Engagement System (MILES) is a training system providing a realistic battlefield environment for soldiers involved in training exercises. The Army developed the original family of MILES devices in the late '70s and early '80s using state-of-the-art technology of that time. MILES is the primary training device for force-on-force training at Army home stations. A MILES system for a soldier includes a laser module (Small Arms Transmitter or SAT) mounted to the barrel of a real weapon, a blank firing adapter, and an integrated receiver with sensors on the helmet and load-bearing vests for the soldiers. The SAT's laser beam is aligned by the solder to the weapon's sights when the SAT is mounted to the weapon. During the training exercise, the soldier aims the weapon on the opposing force soldier using the weapon's standard sights. When a blank shot is fired by the weapon, it causes the laser to fire a coded laser burst in the direction the weapon was aimed. Information contained in the laser pulses includes the player ID and the type of weapon used. If that laser burst is sensed by the receiver of another soldier, the “hit” soldier's gear beacon makes a beeping noise to let them know they are “dead.”
When the weapon fires a blank in the MILES system, unique shock, flash and acoustic signatures are generated. Two of these signatures are decoded to determine a valid event and initiate MILES code transmissions. Once a validated event is detected, the transmitter fires 4 Hit Words and 128 Near-Miss Words. Each word is ˜4 milliseconds (msec) long; the duration for 132 words is 484 msec or 0.484 seconds. The laser beam foot print (typical angular foot print size is 1 mrad to 3 mrad and the maximum size is limited by the specification) needs to illuminate the detector sensor for the full duration of a Hit or Near-Miss Word to be registered by the receiver software as a Kill or Near-Miss.
In the MILES system, there occurs a gross angular weapon movement after the blank has fired that moves the center of the laser foot print away from the sensor. During the time period from trigger pull to firing of the blank and firing the laser, the weapon moves in a semi-repeatable motion. See U.S. Published Patent Application 2004/0005531 for FIGS. 8, 9 & 10. For open bolt weapons like the M240 and M249, the movement and corresponding error is greater after the trigger pull due to the time required for the bolt to close and the impact of the bolt increases the gross angular weapon movement. The shock from the bolt closing and/or the blank firing causes the SAT housing and mounting components to flex and introduce an addition pointing error to the gross weapon movement error which is not repeatable. Also based on the internal construction, the adjustment mechanism can unload (bounce) during the high G event and introduce additional significant pointing errors which is not repeatable.
The sum of these angular pointing errors sources, (gross weapon movement, SAT component flexure and unloading) start at zero values for time zero (trigger pull) and increase over time. The SAT laser needs to be pointing at the opposing soldier's receiver and illuminating it for the 4 msec duration required to transmit the first hit word. The total angular pointing error movement has to less than half the laser angular footprint by the time the SAT has detected the event and finished transmitting the first hit word. The gross weapon angular pointing error is real and part of the normal system operation. The second and third error sources (flexure and unloading) are the problems. They are not part of the normal system operation and need to be minimized or cancelled. To the extent these are not reduced, the training system will depart from reflecting the actual accuracy of the soldier's performance, failing to register otherwise good hits.
The present SAT design approaches do not maintain the initial precise pointing during and after exposure in high G shock and vibration environments.
Various approaches have been proposed to deal with these types of problems. For example, U.S. Published Patent Application 2004/0005531 to Varshneya et al. describes an elaborate and complex system for calibrating misalignment of a weapon-mounted zeroed small arms transmitter (ZSAT) laser beam axis with the shooter line-of-sight (LOS) in a weapon training system, but fails to easily solve the problem. The proposed solution only addresses the repeatable error produced by the dynamic muzzle displacement from the gross weapon movement not the unrepeatable errors from the flexure and unloading errors.
Other types of devices have resulted in additional problems. See for example, U.S. Pat. No. 2,189,766 to Unerti; U.S. Pat. No. 3,476,349 to Smith; U.S. Pat. No. 3,596,863 to Kaspareck; U.S. Pat. No. 4,079,534 to Snyder; U.S. Pat. No. 4,161,076 to Snyder; U.S. Pat. No. 4,212,109 to Snyder; U.S. Pat. No. 4,295,289 to Snyder; U.S. Pat. No. 4,313,272 to Matthews; U.S. Pat. No. 4,686,440 to Nagasawa; U.S. Pat. No. 4,738,044 to Osterhout; U.S. Pat. No. 4,876,816 to Triplett; U.S. Pat. No. 4,916,713 to Gerber; U.S. Pat. No. 4,958,794 to Brewer; U.S. Pat. No. 5,033,219 to Johnson; U.S. Pat. No. 5,299,375 to Heinz; U.S. Pat. No. 6,378,237 to Matthews; U.S. Pat. No. 6,714,564 to Meyers; U.S. Pat. No. 6,793,494 to Deepak; U.S. Pat. No. 6,887,079 to Robertsson; U.S. Pat. No. 7,014,369 to Alcock; U.S. Pat. No. 7,331,137 to Hsu; U.S. Pat. No. 7,418,894 to Ushiwata; U.S. Pat. No. 7,558,168 to Chen; U.S. Pat. No. 7,726,061 to Thummel; U.S. Pat. No. 7,753,549 to Solinsky; U.S. Pat. No. 7,886,644 to Ushiwata; U.S. Pat. No. 7,922,491 to Jones; U.S. Pat. No. 7,926,218 to Matthews; and U.S. Published Patent Applications: 2001/0000130 to Aoki; 2003/0204959 to Hall; 2004/0161197 to Pelletier; 2006/0156556 to Nesch; and 2007/0240355 to Hsu.
Some of the proposed devices intentionally shock isolate by allowing movement of the laser beam axis relative to the weapon to prevent damage to the laser or associated electronics and therefore does not maintain alignment during the shock.
Other proposed devices include multiple parts that move relative to each other when the devices are aligned or boresighted. Due to manufacturing tolerances, there are clearances between mating surfaces that slide relative or mate to each other. There is friction at the sliding and spherical joints due to the preload forces. The tangential friction forces at the contacting surfaces produce bending in the components. During the high G shock or vibration event, the friction at the interface surfaces will go to zero and allow the components to slide and rotate to a force free state. This movement will produce a pointing error relative to the initial alignment. The larger the quality of interfaces, the larger the total pointing error after a shock.
Additional problems with the prior art have included devices having sliding or pivoting joints and geared interfaces that have clearance between the none contacting surfaces can become contaminated which will cause binding or increased friction which will increase the pointing angle error.
Prior art devices have included plural components, threaded rods that translate wedges used for alignment, due to clearances between the mating threaded parts, when the direction and adjustment is reversed, hysteresis will be introduced which is a source of error. After adjustment, during the shock, the stiction will be relieved and the wedge can move over the range of the thread clearance producing a pointing error.
Some of the prior art devices include large and heavy components for a 1 G or manufacturing environment where there is no shock or vibration environment and there is no limitation on size, weight or adjustment type and are cumbersome for field use, difficult to adjust in the field, or the alignment is set at the factory.
Some of the prior art includes devices which cannot maintain alignment or boresight over the wide temperature operating range from the low −40° C. to the high temperature where the barrel of the M240 can exceed 350° C. Over this temperature range, any mismatch in the components CTE (coefficient of thermal expansion) will cause binding or increased clearances at the interfaces which will increase the pointing errors. The component's CTE mismatch will also introduce a bimetallic error as the temperature changes from the initial adjustment temperature.
Still other prior art devices use different types of springs to preload the system against the adjustment stops so a payload does not move away from the stop and produce a dynamic pointing error. The springs used cannot produce enough force in the limited volume to counteract the unloading force.
Thus, the need exists for solutions to the above problems with the prior art.